This is the first progressive report on the crystallization of metals and alloys from liquid and describes the formation of macrostructures in pure aluminum. The controlling variables on forming macrostructures have been determined on the basis of the distance-time curves of the waves of freezing start and end taken from various sets of cooling curves.
High purity, commercial purity and grain refined aluminum have particular types of macrostructures. Movement of the wave of freezing start is rather important than that of freezing end. The starting wave progresses parabolically at the early stage of directional freezing and linearly at the final stage. The transformation of structure from columnar to equiaxial occurs near this transitional point. The substantial location of the structural transformation is dependent on the purity of aluminum or existing stable nuclei. Although most of the thermal variables during freezing are not so important in forming the structure, only the thermal gradient in the liquid just ahead of growing solid is critical for each purity of aluminum. The ratio(linear freezing rate)^1/2/(temperature gradient in liquid) first proposed by Tiller and Rutter probably depends on the temperature gradient to a great degree. The critical temperature gradient for structural transformation also depends on the stability and numbers of existing heterogeneous nuclei. Unfortunately, the substance, numbers, size and distribution of the heterogeneous nuclei have not yet determined particularly on the quantitative basis.

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This report describes effect of various factors on characteristics and mechanical properties of extruded Al-Zn-Mg alloys. Effects of I) Zn, Mg, Mn, Cr and Ti content, II) soaking temperature, III) extruded temperature, and IV) cooling rate after extrusion on mechanical properties of extruded bars with or without heat-treatment are investigated.
Conclusions are as follows:
(1) Effect of Zn and Mg content on mechanical properties of extruded bars are the same as in rolled heat-treated sheets. By cooling in air after extrusion these alloys are effectively quenched so as capable of omitting solid solution heat treatment. The sensitivity to cooling rate from solid solution heat-treatment temperature or extruded temperature increases with Mg content, but does not change with Zn content. Addition of Mn and Cr to Al-5% Zn-1% Mg alloy have very little effect on the sensitivity of this alloy to rates of cooling.
(2) When Al-Zn-Mg alloys containing Mn are soaked at 400-450°C before extrusion, extruded bars of these alloys have fine extruded texture with substructure, which improves remarkably tensile properties of extruded bars.
(3) At the backend of extruded bars extremely high tensile properties are obtained on Al-5% Zn-1% Mg-0.35% Mn alloys, soaked at 400-450°C and extruded at 400°C, or Al-5% Zn-1% Mg-0.2% Mn alloys, soaked at 450°C and extruded at 450°C.
(4) Improvement of tensile properties by Mn addition can be seen in natural age hardening condition but not in artificial age hardening.
(5) By increasing the rate of cooling after extrusion tensile properties of extruded Al-5% Zn-1%Mg alloys are improved, but alloys containing Mn are not so improved as alloys containing no Mn.
(6) Extruded bars of Al-5% Zn-1%Mg alloys have low tensile strength at an angle of 22.5°to the extruded direction.

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Since Harrington's report in 1949, recrystallization characteristics of Al-Zr alloys have been investigated by many metallurgists in our country. And now, some patent alloys of Al-Zr base are reported. But, on account of the difficulty in obtaining equilibrium structure of Al-Zr system in phase diagram and high chemical activity of Zr-rich phase in open atmosphere, behaviour of Zr in aluminium is not fully understood as yet. So we tried to reevaluate the effect of Zr addition to aluminium of different grades, and studied ageing and recrystallization phenomena of Al-Zr alloys by hardness, electrical resistance, and transmission electron microscopic methods.
The results are summarized as follows:
1. Even by normal melting and casting conditions. Zr addition up to 0.15-0.2wt. % is sufficient to level up the recrystallization temperature of aluminium (99.99-99.7% grades) by at least 100°C.
2. Al-Zr alloys seem to have little response to ageing treatment, at least in practical meaning.
3. Zr is effective in improving recrystallization characteristics of cold worked aluminium by making small angle boundaries more stable and prohibiting their migration in high temperature region.

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The effect of magnesium on the mechanical properties and microstructures of Al-Si-Cr alloys, containing 8.5% silicon and 0.3% chromium, were studied.
Addition of 1.0% magnesium improves remarkably the mechanical properties of these alloys.
After T₆ treatment, various compounds are precipitated. These are T(Mg, Cr) compound, α(Cr, Si) compound, β(Cr, Si) compound and Mg₂Si. Mechanical properties are improved by the precipitation of these compounds, and the tensile strength of this alloy, which was cast in sand mould and T₆ treated, comes to 35kg/mm².

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As the copper silumin (ADC12, ADC13) casting, which is one of die casting aluminium alloys, has a good castability and a good mechanical property, it is used in many field. But, it is well known that the casting condition and the mechanical property of the castings are affected largely by the iron content as an impurity in the copper silumin and that, especially, the hard-spot, which interferes frequently with the cutting, is looked upon to be result from an iron content. As the machinability of the copper silumin castings is searched by the authors, and it is expected that the machinability is very changeable by the condition of die casting and the chemical composition, especially, the content of impurities, i. e., an iron and others, even in same cutting condition, the mechanical property and the machinability with the going of the shot number is examined in early stage and stationary stage of the die casting as one of their foundamental experiments. That is, immediately after the commencement of die casting, the temperature of dies and other parts of the machine is not so rising, while, as the operation goes, the temperature naturally goes up, if so, the mechanical properties may also be different between the casting in early stages and stationary stages of die casting. On the castings, e. g., the wheel hubs for auto-cycle parts, the machinability in turning and drilling is discussed by the cutting resistance, the surface roughness and others. As the results, the machinability decreases with the rise of the cutting resistance in the fiftieth shot casting and as the operation goes stationary, the machinability increases again decreasing with the cutting resistance. But, their changes is not so distinctly, and it can not be said that the influence of shot number on the machinability is large.
This investigation was done with the fund afforded by Scholarship Committee of the Institute of Light Metal Foundation, for which we are extremly grateful.

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Some mechanical properties at room and elevated temperatures of extrusions made of jet-atomized magnesium-1wt% aluminium alloy powder, magnesium-0.6wt% zirconium alloy powder and simultaneous extrusion of 50/50 mixture of these two powders have been investigated. The powder-extrusions, in comparison with cast-billet extrusion, have finer grains and higher hardness than that of the latter in both as-extruded and annealed states. They also have at all testing temperatures higher ultimate tensile strength, yield strength and especially exhibit a higher creep resistance at 350-450°C but lower elongation. This seems to be very much concerned with the amount of oxide dispersed which is also attributable to poor ductility of the powder-extrusions. The metallographic observation of cavities in creep-ruptured specimens shows that the cavities originate preferentially at the longitudinal grain boundaries, which were formerly the surface of the powders and where oxide particles exist, rather than at the transverse grain boundaries. The cavities grow toward the transverse direction and continuation of cavities results in fracture of specimens. Some consideration of the interaction between dislocations and oxide particles have also been made.

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